This invention relates to a semiconductor device, which can improve the barrier properties of a diffusion prevention film for preventing the mutual diffusion between silicon and metal and also between metal and metal and ensure satisfactory electric conductivity.
In semiconductor devices, many contact sections or junctions between silicon and metal and between different metals are formed. When such a junction is elevated to a high temperature during manufacture of the semiconductor device, mutual diffusion between silicon and metal or between different metals takes place. In order to prevent mutual diffusion, various diffusion prevention films have been studied. Among the diffusion prevention films that have been studied, the TiN film is thought to be most promising.
Now, an application of the TiN film as a mutual diffusion prevention film between a silicon diffusion layer and an aluminum film will be described. As shown in FIG. 1A, N-type diffusion layer 2 having a junction depth of 0.20 .mu.m is formed in P-type silicon substrate 1. Silicon oxide film 7 is formed by the CVD process on the surface of substrate 1. Then, oxide film 7 is selectively removed using a photoresist (not shown) as a mask to expose corresponding portions of diffusion layer 2. Thereafter, titanium nitride film 3 having a thickness of 1,000 angstroms is formed on diffusion layer 2 and oxide film 7. Then, an aluminum film 4 with a thickness of 1 .mu.m is formed on titanium nitride film 3.
Titanium nitride film 3 is formed in a sputtering process in Ar/N.sub.2 mixture plasma (N.sub.2 :60%) using a titanium target.
Aluminum film 4 and titanium nitride film 3 are patterned to form a diode, and the junction leak current therein is measured.
The resultant structure is annealed at 500.degree. C. for 30 minutes before measurement of the junction leak current, and an abnormal junction leak current is measured.
When a defective portion is observed in detail, a small alloy pit was found in diffusion region 2. It is found that the junction is damaged by this alloy pit due to the following reason. Barrier properties of titanium nitride (TiN) film 3 are lost by a certain reason, and mutual diffusion between aluminum (Al) and silicon (Si) locally occurs.
The cause of the alloy pit will be described with reference to FIG. 1B. A small amount of non-reacted titanium 5 is present in titanium nitride (TiN) film 3. Titanium nitride film 3 is polycrystalline and non-reacted titanium 5 gathers on a grain boundary of the crystal grains constituting titanium nitride film 3. Al-Si mutual diffusion is accelerated through non-reacted titanium 5 gathering on the grain boundary, and alloy pit 6 is formed. As a result, junction leakage occurs.